U.S. patent application number 13/648574 was filed with the patent office on 2013-10-10 for nozzle design to reduce fretting.
This patent application is currently assigned to PRATT & WHITNEY CANADA CORP.. The applicant listed for this patent is PRATT & WHITNEY CANADA CORP.. Invention is credited to Saeid Oskooei.
Application Number | 20130263603 13/648574 |
Document ID | / |
Family ID | 42630102 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130263603 |
Kind Code |
A1 |
Oskooei; Saeid |
October 10, 2013 |
NOZZLE DESIGN TO REDUCE FRETTING
Abstract
A method of designing a fuel nozzle of a gas turbine engine to
reduce fretting thereof during use, including establishing an
initial nozzle design, determining a first natural frequency of
that design and a running frequency range of the gas turbine
engine, and increasing a first transverse dimension of the stem
member of the nozzle across a length of a portion thereof adjacent
the inlet end until the first natural frequency of the nozzle is
outside the running range, while a second transverse dimension of
the portion remains at least substantially unchanged across the
length thereof.
Inventors: |
Oskooei; Saeid; (Toronto,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PRATT & WHITNEY CANADA CORP.; |
|
|
US |
|
|
Assignee: |
PRATT & WHITNEY CANADA
CORP.
Longueuil
CA
|
Family ID: |
42630102 |
Appl. No.: |
13/648574 |
Filed: |
October 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12389631 |
Feb 20, 2009 |
8308076 |
|
|
13648574 |
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Current U.S.
Class: |
60/740 |
Current CPC
Class: |
F23R 3/283 20130101;
F05D 2260/96 20130101; F23R 2900/00005 20130101; F02C 7/22
20130101 |
Class at
Publication: |
60/740 |
International
Class: |
F02C 7/22 20060101
F02C007/22 |
Claims
1. A fuel nozzle for a gas turbine engine, the nozzle comprising a
monolithic stem member having an inlet end with at least one inlet
for connection to a fuel supply, an outlet end with at least one
outlet for connection to a spray tip assembly, and a central
portion extending between the inlet and outlet ends, the stem
member having at least one fuel conduit extending therethrough in
connection with the inlet end and the outlet end, the stem member
having a longitudinal axis and first and second transverse axes
defined at least substantially perpendicularly to the longitudinal
axis, a first outer dimension of the central portion defined
parallel to the first transverse axis increasing from a first point
located between the inlet and outlet ends to a second point
adjacent the inlet end, a second outer dimension of the central
portion defined parallel to the second transverse axis remaining at
least substantially constant between the first and second
points.
2. The fuel nozzle as defined in claim 1, wherein the first
transverse dimension is increased at a progressively larger rate
between the first and second points such as to obtain a flat
tapered profile with a maximum located at the second point.
3. The fuel nozzle as defined in claim 1, wherein the first
transverse dimension increases between the first and second points
in an at least substantially symmetrical manner with respect to the
longitudinal axis.
4. The fuel nozzle as defined in claim 1, wherein the first and
second transverse dimensions are at least substantially
perpendicular to one another.
5. The fuel nozzle as defined in claim 1, wherein the central
portion includes at least one longitudinal slot defined in an outer
surface thereof and sealed by a cover plate to define one of the at
least one fuel conduits, the cover plate extending at least
substantially perpendicularly to the second transverse axis.
6. The fuel nozzle as defined in claim 1, wherein a distance
between the first point and the inlet end corresponds to less than
half of a length of the central portion.
7. The fuel nozzle as defined in claim 1, wherein the stem member
has an at least substantially rectangular cross-section, the first
and second transverse axes being defined perpendicularly to one
another, the second transverse axis being defined perpendicularly
to opposed outer surfaces of the stem member.
8. The fuel nozzle as defined in claim 7, wherein the opposed outer
surfaces each include a longitudinal slot defined therein in
connection with the inlet and the outlet and sealed by a plate
member to define one of the at least one fuel conduits.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Divisional of U.S. patent
application Ser. No. 12/239,264 filed Sep. 26, 2008, the entire
content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The application relates generally to a fuel nozzle for gas
turbine engine and, more particularly, to such a fuel nozzle in
which fretting is reduced.
BACKGROUND OF THE ART
[0003] Fuel nozzles generally include a stem portion having an
inlet coupled to a fuel source and an outlet coupled to a spray tip
assembly for spraying or atomizing fuel into the combustion
chamber. The spray tip assembly is generally received through the
combustor wall floating collar, and vibrations caused by the engine
in use can cause friction between the spray tip assembly and the
combustor wall floating collar, thus causing fretting of this
element of the fuel nozzle. Fuel nozzles, or parts thereof
undergoing fretting, generally need to be regularly replaced to
compensate for this damage. Such replacements increase time and
costs of maintenance of the engine.
SUMMARY
[0004] In one aspect, there is provided a method of providing a
fuel nozzle of a gas turbine engine to reduce fretting thereof
during use, the method comprising establishing an initial nozzle
design for a one-piece stem member having an inlet end for
connection to a fuel supply, an outlet end for connection to a
spray tip assembly and a central portion extending between the
inlet and outlet ends and including and at least one fuel conduit
defined therethrough in communication with the inlet and outlet
ends, the central portion including a section defined adjacent the
inlet end and extending along only part of a length of the central
portion, determining a first natural frequency of the initial
nozzle design, determining a running frequency range of the gas
turbine engine, increasing a first transverse dimension of the stem
member across a length of said section until the first natural
frequency of the fuel nozzle is outside the running frequency range
while a second transverse dimension of said section remains at
least substantially unchanged across the length thereof, the first
and second transverse dimensions being defined along different
directions extending perpendicularly to a longitudinal axis of the
stem member, and providing the one-piece stem member including the
section with the increased first transverse dimension and the at
least substantially unchanged second transverse dimension.
[0005] In another aspect, there is provided a method of reducing
fretting of fuel nozzles in a gas turbine engine, the method
comprising selecting a first stem member of a fuel nozzle installed
in the gas turbine engine, selecting a second stem member including
at least one fuel conduit similar to that of the first stem member,
the stem members each having an inlet end adapted to be connected
to a fuel supply, an outlet end, a central portion extending
between the inlet and outlet ends, and a section corresponding to
only part of the central portion and adjacent the inlet end, at
least the second stem member being made of a single piece, the
second stem member having a first transverse dimension defined
across a length of said section greater than that of the first stem
member such that the fuel nozzle with the second stem member has a
first natural frequency different than that with the first stem
member and outside a running range of the gas turbine engine, the
first and second stem members having similar or identical second
transverse dimensions defined across the length of the section, the
first and second transverse dimensions of each stem member being
defined along different directions extending perpendicularly to a
longitudinal axis thereof, and substituting the first stem member
by the second stem member.
[0006] In a further aspect, there is provided a fuel nozzle for a
gas turbine engine, the nozzle comprising a monolithic stem member
having an inlet end with at least one inlet for connection to a
fuel supply, an outlet end with at least one outlet for connection
to a spray tip assembly, and a central portion extending between
the inlet and outlet ends, the stem member having at least one fuel
conduit extending therethrough in connection with the inlet end and
the outlet end, the stem member having a longitudinal axis and
first and second transverse axes defined at least substantially
perpendicularly to the longitudinal axis, a first outer dimension
of the central portion defined parallel to the first transverse
axis increasing from a first point located between the inlet and
outlet ends to a second point adjacent the inlet end, a second
outer dimension of the central portion defined parallel to the
second transverse axis remaining at least substantially constant
between the first and second points.
DESCRIPTION OF THE DRAWINGS
[0007] Reference is now made to the accompanying figures in
which:
[0008] FIG. 1 is a schematic cross-sectional view of a gas turbine
engine;
[0009] FIG. 2 is a perspective view of part of a fuel nozzle of the
prior art;
[0010] FIG. 3 is a perspective view of a modified stem member for a
fuel nozzle which can be used in a gas turbine engine such as that
shown in FIG. 1; and
[0011] FIG. 4 is a side view of the stem member of FIG. 3 with a
corresponding heat shield shown in cross-section.
DETAILED DESCRIPTION
[0012] FIG. 1 illustrates a gas turbine engine 10 of a type
preferably provided for use in subsonic flight, generally
comprising in serial flow communication a fan 12 through which
ambient air is propelled, a compressor section 14 for pressurizing
the air, a combustor 16 in which the compressed air is mixed with
fuel and ignited for generating an annular stream of hot combustion
gases, and a turbine section 18 for extracting energy from the
combustion gases.
[0013] FIG. 2 illustrates part of a fuel nozzle 20 of the prior
art, for example such as shown in U.S. Pat. No. 6,141,968 which is
incorporated herein in reference. The fuel nozzle 20 includes a
stem member 22 having an inlet end 24 with one or more inlets for
connection to a fuel supply (not shown), an outlet end 26 with one
or more outlets for connection to a spray tip assembly (not shown),
and a thinner central portion 28 extending therebetween.
Longitudinal slots 30 (only one of which is visible) are defined on
opposite outer surfaces 32 of the central portion 28 of the stem
member 22, each slot 30 being in communication with the inlet and
outlet ends 24, 26. Each slot 30 is sealed by a respective cover
plate 34, such that each slot 30 defines a fuel conduit through the
stem member 22. Longitudinally aligned holes 36 are defined in the
central portion 28 of the stem member 22, i.e., between the two
longitudinal slots 30, for lightening purposes. These holes 36
extend transversally with respect to the longitudinal axis L of the
stem member 22. A tubular heat shield 40 is provided for protecting
the stem member 22, and extends between outer surfaces of the inlet
and outlet ends 24, 26.
[0014] In some instances, the first natural frequency of the fuel
nozzle 20 partly illustrated in FIG. 2 may fall within the running
frequency range of the gas turbine engine in which the fuel nozzle
20 is used, which is undesirable. As such, it is desirable to
increase the first natural frequency of the fuel nozzle such that
it is outside this running frequency range of the engine. As a
common practice, the first natural frequency of the fuel nozzle
should be higher than the engine rotor running frequency with an
acceptable margin therebetween. Changing the first natural
frequency of the fuel nozzle 20 away from the running range may
advantageously reduce fretting, and as such the frequency at which
portions of the fuel nozzle 20 need to be replaced.
[0015] Reference is made to FIG. 3, where a modified stem member
122 for a fuel nozzle is shown. The modified stem member 122, when
used in place of the first stem member 22, increases the first
natural frequency of the fuel nozzle and as such brings the first
natural frequency of the fuel nozzle outside of the running range
of the engine.
[0016] The modified stem member 122 inlet and outlet ends 124, 126
similar or identical to that of the first stem member 22. The
modified stem member 122 also includes a thinner central portion
128 interconnecting the inlet and outlet ends 124, 126. The
modified stem member 122 is monolithic, i.e. formed as a unitary
piece of material, and also includes longitudinal slots 130 (only
one of which is visible) defined on opposite outer surfaces 132 of
the central portion 128, each slot 130 being in communication with
the inlet and outlet ends 124, 126. Each slot 130 is sealed by a
respective cover plate (not shown), such that each slot 130 defines
a fuel conduit through the modified stem member 122. When the
modified stem member 122 is used in replacement of the first stem
member 22, the two preferably include similar or identical fuel
conduits defined therein through the slots 30, 130.
[0017] A first section or part 142 of the central portion 128 of
the modified stem member 122, which is defined adjacent the outlet
end 126, is similar or identical to that of the first stem member
22. A second section or part 144 of the central portion 128 of the
modified stem member 122, which is defined between the first part
142 and the inlet end 124, has an increased mass with respect to
that of the first stem member 22, thus causing an increased natural
frequency for the modified stem member 122 and corresponding fuel
nozzle.
[0018] Two different transverse axes T1, T2 can be defined
perpendicularly to the longitudinal axis L of each stem member 22,
122. In the embodiment shown, the central portion of each stem
member 22, 122 has an at least substantially rectangular cross
section, the two transverse axes T1, T2 are defined perpendicularly
to each other, and the second transverse axis T2 is defined
perpendicularly to the opposed outer surfaces 32, 132 of the stem
member 22, 122 receiving the cover plates. However, in an alternate
embodiment, the transverse axes T1, T2 can be defined
non-perpendicularly to each other.
[0019] Throughout the second part 148 of the central portion 128 of
the modified stem member 122, a first outer dimension D1 defined
parallel to the first transverse axis T1 is increased at a
progressively larger rate from a first point P1 defined at the end
of the first part 142 to a second point P2 defined adjacent the
inlet end 124. As such, the second part 148 of the central portion
128 has a tapered shape, with a maximum thickness located at the
second point P2 adjacent the inlet end 124, thus allowing the
weight increase of the modified stem member 122 when compared to
the first stem member 22 to be minimized for a given increase in
first natural frequency. However, throughout the second part 148 of
the central portion 128 of the modified stem member 122, a second
outer dimension D2 defined parallel to the second transverse axis
T2 remains at least substantially unchanged across the length
thereof, and in a particular embodiment, is at least substantially
constant across the length of the central portion 128. Increasing
the outer dimension of the stem member along only part of its
perimeter further minimizes the weight increase for a given
increase in natural frequency.
[0020] By comparison, the first and second outer dimensions D1, D2
of the first stem member 22 of FIG. 2 are both at least
substantially constant across the length of the central portion 28
of the stem member 22.
[0021] In a particular embodiment, the first outer dimension D1 of
the modified stem member 122 is increased such that the second part
144 has an at least substantially triangular shape defined by flat
tapered outer surfaces. In a particular embodiment, the first outer
dimension D1 is increased at least substantially symmetrically with
respect to the longitudinal axis L.
[0022] In a particular embodiment, the cover plates (not shown)
sealingly connected to the modified stem member 122 are thicker
than the cover plates 34 sealingly connected to the first stem
member 22, for example having twice the thickness of the cover
plates 34 received on the first stem member 22, to further increase
the stiffness and the natural frequency of the fuel nozzle.
[0023] In a particular embodiment, the second part 144 of the
central portion 128, where the thickness of the stem member 122 is
increased, is optimized to provide the necessary frequency increase
with minimum weight increase. In one example, the length of the
second part 144 of the central portion 128 corresponds to less than
half the length of the central portion 128 of the stem member
122.
[0024] The modified stem member 122 also includes longitudinally
aligned holes 136 defined in the central portion 128 of the stem
member 122 for lightening purposes; however these holes are omitted
in most of the second part 144 of the central portion 128.
[0025] As such, upon designing a fuel nozzle for a particular gas
turbine engine, the dimensions for a fuel nozzle 20 such as partly
shown in FIG. 2 can be determined according to appropriate methods.
A running frequency range for the specific gas turbine engine 10 is
then determined. In the case where the first natural frequency of
the nozzle 20 is within or too close to the determined running
range, the first transverse dimension D1 of the second part 144 of
the central portion 128 of the modified stem member 122 is
increased across its length while keeping the second transverse
dimension D2 at least substantially unchanged, as described above,
until the first natural frequency of the fuel nozzle 20 reaches an
acceptable value outside the running frequency range. This can be
done according to an iterative process, verifying the first natural
frequency of the fuel nozzle for example through experimentation,
e.g. using strain gauge tests on fuel nozzles installed in the gas
turbine engine, using adequate modeling software, etc.
[0026] Referring to FIG. 4, the increase of the first dimension D1
is preferably limited to allow the central portion 128 of the
modified stem member 122 to remain contained inside the same
envelope 43 defined by the heat shield 40 of the first stem member
22. In the embodiment shown, the heat shield 40 is tubular and
extends between outer surfaces of the inlet and outlet ends 24, 26,
and as such the increase of the first dimension D1 is limited such
that the central portion 128 of the modified stem member 122 does
not extend outwardly beyond the inlet and outlet ends 124, 126. As
such, a same or similar heat shield can be installed around the
modified stem member 122 when compared to the first stem member 22,
and the modified and first stem members 22, 122 may appear
identical once the heat shield 40 is installed.
[0027] The above description is meant to be exemplary only, and one
skilled in the art will recognize that changes may be made to the
embodiments described without departing from the scope of the
invention disclosed. For example, the dimensions variations applied
between the modified stem member 122 and the first stem member 22
can be similarly applied to different types of stem members,
including, but not limited to, stem members having tubular fuel
conduits defined therethrough, stem members having a different
shape, and stem members which are integral with other portions of
the fuel nozzle (e.g. the spray tip assembly). Still other
modifications which fall within the scope of the present invention
will be apparent to those skilled in the art, in light of a review
of this disclosure, and such modifications are intended to fall
within the appended claims.
* * * * *